Apparatus and method for hypersensitivity detection of magnetic field

ABSTRACT

A system for magnetic detection includes a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers, a radio frequency (RF) excitation source configured to provide RF excitation to the NV diamond material, an optical excitation source configured to provide optical excitation to the NV diamond material, an optical detector configured to receive an optical signal emitted by the NV diamond material, and a controller. The optical signal is based on hyperfine states of the NV diamond material. The controller is configured to detect a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of priority from U.S. Provisional Patent Application No. 62/257,988, filed Nov. 20, 2015, which is incorporated herein by reference in its entirety. This application is related to co-pending U.S. Patent Application filed Jan. 21, 2016, titled “APPARATUS AND METHOD FOR CLOSED LOOP PROCESSING FOR A MAGNETIC DETECTION SYSTEM” (Atty. Dkt. No. 111423-1041), which is incorporated by reference herein in its entirety.

FIELD

The present disclosure generally relates to magnetometers, and more particularly, to hypersensitivity detection using hyperfine gradient detection.

BACKGROUND

Atomic-sized nitrogen-vacancy (NV) centers in diamond lattices have been shown to have excellent sensitivity for magnetic field measurement and enable fabrication of small magnetic sensors that can readily replace existing-technology (e.g., Hall-effect, SERF, SQUID, or the like) systems and devices. Nitrogen vacancy diamond (DNV) magnetometers are able to sense extremely small magnetic field variations by changes in the diamond's red photoluminescence that relate, through the gradient of the luminescent function, to frequency and thereafter to magnetic field through the Zeeman effect.

SUMMARY

According to certain embodiments, a system for magnetic detection may include a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers, a radio frequency (RF) excitation source configured to provide RF excitation to the NV diamond material, an optical excitation source configured to provide optical excitation to the NV diamond material, an optical detector configured to receive an optical signal emitted by the NV diamond material, wherein the optical signal is based on hyperfine states of the NV diamond material, and a controller. The controller is configured to detect a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.

According to one aspect, a controller may be configured to detect a point of the largest gradient of the optical signal based on the hyperfine states.

According to one aspect, a controller may be further configured to detect a movement of the gradient of the optical signal based on the hyperfine states emitted by the NV diamond material, and compute a total incident magnetic field at the NV diamond material based on the movement of the gradient.

According to one aspect, an RF excitation source may be configured to provide the RF excitation at a low power.

According to one aspect, a system may further include a magnetic field generator configured to generate a bias magnetic field, and the controller is further configured to detect a plurality of gradients of the optical signal based on the hyperfine states for a plurality of NV center orientations.

According to one aspect, a system may further include a magnetic field generator configured to generate a magnetic field, and the controller is further configured to control the magnetic field generator to generate a bias magnetic field and to detect a plurality of gradients of the optical signal based on the hyperfine states for a plurality of NV center orientations.

According to other embodiments, a system for magnetic detection may include a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers, means for providing a radio frequency excitation to the NV diamond material, means for providing optical excitation to the NV diamond material, means for receiving an optical signal emitted by the NV diamond material, wherein the optical signal is based on hyperfine states of the NV diamond material, and means for detecting a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.

According to one aspect, a means for detecting a gradient of the optical signal based on the hyperfine states may detect a point of the largest gradient of the optical signal.

According to one aspect, a system may further include means for generating a bias magnetic field, and the means for detecting a gradient of the optical signal based on the hyperfine states detects a plurality of gradients of the optical signal for a plurality of NV center orientations.

According to other embodiments, a method for increasing measurement sensitivity of a magnetic detection system having a nitrogen vacancy (NV) diamond material may comprise a plurality of NV centers including applying RF excitation to the NV diamond material, applying optical excitation to the NV diamond material, measuring an optical signal emitted by the NV diamond material, wherein the optical signal emitted by the NV diamond is based on hyperfine states of the NV diamond material, and detecting a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.

According to one aspect, a method may further include detecting a movement of the gradient of the optical signal based on the hyperfine states emitted by the NV diamond material, and computing a total incident magnetic field at the NV diamond material based on the movement of the gradient.

According to one aspect, a detected gradient may be a point of the largest gradient of the optical signal based on the hyperfine states.

According to one aspect, an RF excitation may be applied at a low power.

According to one aspect, an RF excitation may be applied at a power ranging from about 1 to about 10 W/mm².

According to one aspect, a method may further include applying a bias magnetic field, and detecting a plurality of gradients of the optical signal based on the hyperfine states for a plurality of NV center orientations.

According to other embodiments, a system for magnetic detection may include a magneto-optical defect center material comprising a plurality of magneto-optical defect centers, a radio frequency (RF) excitation source configured to provide RF excitation to the magneto-optical defect center material, an optical excitation source configured to provide optical excitation to the magneto-optical defect center material, an optical detector configured to receive an optical signal emitted by the magneto-optical defect center material, wherein the optical signal is based on hyperfine states of the magneto-optical defect center material, and a controller configured to detect a gradient of the optical signal based on the hyperfine states emitted by the magneto-optical defect center material.

According to one aspect, a controller may be configured to detect a point of the largest gradient of the optical signal based on the hyperfine states.

According to one aspect, a controller may be further configured to detect a movement of the gradient of the optical signal based on the hyperfine states emitted by the magneto-optical defect center material, and compute a total incident magnetic field at the magneto-optical defect center material based on the movement of the gradient.

According to one aspect, an RF excitation source may be configured to provide the RF excitation at a low power.

According to one aspect, a system may further include a magnetic field generator configured to generate a bias magnetic field, and the controller is further configured to detect a plurality of gradients of the optical signal based on the hyperfine states for a plurality of magneto-optical defect center orientations.

According to one aspect, a system may further include a magnetic field generator configured to generate a magnetic field, and the controller is further configured to control the magnetic field generator to generate a bias magnetic field and to detect a plurality of gradients of the optical signal based on the hyperfine states for a plurality of magneto-optical defect center orientations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one orientation of an NV center in a diamond lattice.

FIG. 2 is an energy level diagram showing energy levels of spin states for the NV center.

FIG. 3 is a schematic illustrating an NV center magnetic sensor system.

FIG. 4 is a graph illustrating a fluorescence as a function of an applied RF frequency of an NV center along a given direction for a zero magnetic field.

FIG. 5 is a graph illustrating the fluorescence as a function of an applied RF frequency for four different NV center orientations for a non-zero magnetic field.

FIG. 6 is a schematic diagram illustrating a magnetic field detection system according to an embodiment of the present invention.

FIG. 7 is a graph illustrating a fluorescence as a function of an applied RF frequency for an NV center orientation in a non-zero magnetic field and a gradient of the fluorescence as a function of the applied RF frequency.

FIG. 8 is an energy level diagram showing a hyperfine structure of spin states for the NV center.

FIG. 9 is a graph illustrating a fluorescence as a function of an applied RF frequency for an NV center orientation in a non-zero magnetic field with hyperfine detection and a gradient of the fluorescence as a function of the applied RF frequency.

DETAILED DESCRIPTION

Aspects of the disclosure relates to apparatuses and methods for elucidating hyperfine transition responses to determine an external magnetic field acting on a magnetic detection system. The hyperfine transition responses exhibit a steeper gradient than the gradient of aggregate Lorentzian responses measured in conventional systems, which can be up to three orders of magnitude larger. The steeper gradient exhibited by the hyperfine transition responses thus allow for a comparable increase in measurement sensitivity in a magnetic detection system. By utilizing the largest gradient of the hyperfine responses for measuring purposes, external magnetic fields may be detected more accurately, especially low magnitude and/or rapidly changing fields.

The NV Center, its Electronic Structure, and Optical and RF Interaction

The NV center in a diamond comprises a substitutional nitrogen atom in a lattice site adjacent a carbon vacancy as shown in FIG. 1. The NV center may have four orientations, each corresponding to a different crystallographic orientation of the diamond lattice.

The NV center may exist in a neutral charge state or a negative charge state. Conventionally, the neutral charge state uses the nomenclature NV⁰, while the negative charge state uses the nomenclature NV, which is adopted in this description.

The NV center has a number of electrons, including three unpaired electrons, each one from the vacancy to a respective of the three carbon atoms adjacent to the vacancy, and a pair of electrons between the nitrogen and the vacancy. The NV center, which is in the negatively charged state, also includes an extra electron.

The NV center has rotational symmetry, and as shown in FIG. 2, has a ground state, which is a spin triplet with ³A₂ symmetry with one spin state m_(s)=0, and two further spin states m_(s)=+1, and m_(s)=−1. In the absence of an external magnetic field, the m_(s)=±1 energy levels are offset from the m_(s)=0 due to spin-spin interactions, and the m_(s)=±1 energy levels are degenerate, i.e., they have the same energy. The m_(s)=0 spin state energy level is split from the m_(s)=±1 energy levels by an energy of 2.87 GHz for a zero external magnetic field.

Introducing an external magnetic field with a component along the NV axis lifts the degeneracy of the m_(s)=±1 energy levels, splitting the energy levels m_(s)=±1 by an amount 2 gμ_(B)Bz, where g is the g-factor, μ_(B) is the Bohr magneton, and Bz is the component of the external magnetic field along the NV axis. This relationship is correct to a first order and inclusion of higher order corrections is straightforward matter and will not affect the computational and logic steps in the systems and methods described below.

The NV center electronic structure further includes an excited triplet state ³E with corresponding m_(s)=0 and m_(s)=±1 spin states. The optical transitions between the ground state ³A₂ and the excited triplet ³E are predominantly spin conserving, meaning that the optical transitions are between initial and final states that have the same spin. For a direct transition between the excited triplet ³E and the ground state ³A₂, a photon of red light is emitted with a photon energy corresponding to the energy difference between the energy levels of the transitions.

There is, however, an alternative non-radiative decay route from the triplet ³E to the ground state ³A₂ via intermediate electron states, which are thought to be intermediate singlet states A, E with intermediate energy levels. Significantly, the transition rate from the m_(s)=±1 spin states of the excited triplet ³E to the intermediate energy levels is significantly greater than the transition rate from the m_(s)=0 spin state of the excited triplet ³E to the intermediate energy levels. The transition from the singlet states A, E to the ground state triplet ³A₂ predominantly decays to the m_(s)=0 spin state over the m_(s)=±1 spins states. These features of the decay from the excited triplet ³E state via the intermediate singlet states A, E to the ground state triplet ³A₂ allows that if optical excitation is provided to the system, the optical excitation will eventually pump the NV center into the m_(s)=0 spin state of the ground state ³A₂. In this way, the population of the m_(s)=0 spin state of the ground state ³A₂ may be “reset” to a maximum polarization determined by the decay rates from the triplet ³E to the intermediate singlet states.

Another feature of the decay is that the fluorescence intensity due to optically stimulating the excited triplet ³E state is less for the m_(s)=±1 states than for the m_(s)=0 spin state. This is so because the decay via the intermediate states does not result in a photon emitted in the fluorescence band, and because of the greater probability that the m_(s)=±1 states of the excited triplet ³E state will decay via the non-radiative decay path. The lower fluorescence intensity for the m_(s)=±1 states than for the m_(s)=0 spin state allows the fluorescence intensity to be used to determine the spin state. As the population of the m_(s)=±1 states increases relative to the m_(s)=0 spin, the overall fluorescence intensity will be reduced.

The NV Center, or Magneto-Optical Defect Center, Magnetic Sensor System

FIG. 3 is a schematic diagram illustrating a conventional NV center magnetic sensor system 300 that uses fluorescence intensity to distinguish the m_(s)=±1 states, and to measure the magnetic field based on the energy difference between the m_(s)=+1 state and the m_(s)=−1 state. The system 300 includes an optical excitation source 310, which directs optical excitation to an NV diamond material 320 with NV centers. The system further includes an RF excitation source 330, which provides RF radiation to the NV diamond material 320. Light from the NV diamond may be directed through an optical filter 350 to an optical detector 340.

The RF excitation source 330 may be a microwave coil, for example. The RF excitation source 330, when emitting RF radiation with a photon energy resonant with the transition energy between ground m_(s)=0 spin state and the m_(s)=+1 spin state, excites a transition between those spin states. For such a resonance, the spin state cycles between ground m_(s)=0 spin state and the m_(s)=+1 spin state, reducing the population in the m_(s)=0 spin state and reducing the overall fluorescence at resonances. Similarly, resonance occurs between the m_(s)=0 spin state and the m_(s)=−1 spin state of the ground state when the photon energy of the RF radiation emitted by the RF excitation source is the difference in energies of the m_(s)=0 spin state and the m_(s)=−1 spin state, or between the m_(s)=0 spin state and the m_(s)=+1 spin state, there is a decrease in the fluorescence intensity.

The optical excitation source 310 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 310 induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 320 is directed through the optical filter 350 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the detector 340. The optical excitation light source 310, in addition to exciting fluorescence in the diamond material 320, also serves to reset the population of the m_(s)=0 spin state of the ground state ³A₂ to a maximum polarization, or other desired polarization.

For continuous wave excitation, the optical excitation source 310 continuously pumps the NV centers, and the RF excitation source 330 sweeps across a frequency range that includes the zero splitting (when the m_(s)=±1 spin states have the same energy) energy of 2.87 GHz. The fluorescence for an RF sweep corresponding to a diamond material 320 with NV centers aligned along a single direction is shown in FIG. 4 for different magnetic field components Bz along the NV axis, where the energy splitting between the m_(s)=−1 spin state and the m_(s)=+1 spin state increases with Bz. Thus, the component Bz may be determined. Optical excitation schemes other than continuous wave excitation are contemplated, such as excitation schemes involving pulsed optical excitation, and pulsed RF excitation. Examples of pulsed excitation schemes include Ramsey pulse sequence, and spin echo pulse sequence.

In general, the diamond material 320 will have NV centers aligned along directions of four different orientation classes. FIG. 5 illustrates fluorescence as a function of RF frequency for the case where the diamond material 320 has NV centers aligned along directions of four different orientation classes. In this case, the component Bz along each of the different orientations may be determined. These results, along with the known orientation of crystallographic planes of a diamond lattice, allow not only the magnitude of the external magnetic field to be determined, but also the direction of the magnetic field.

While FIG. 3 illustrates an NV center magnetic sensor system 300 with NV diamond material 320 with a plurality of NV centers, in general, the magnetic sensor system may instead employ a different magneto-optical defect center material, with a plurality of magneto-optical defect centers. The electronic spin state energies of the magneto-optical defect centers shift with magnetic field, and the optical response, such as fluorescence, for the different spin states is not the same for all of the different spin states. In this way, the magnetic field may be determined based on optical excitation, and possibly RF excitation, in a corresponding way to that described above with NV diamond material.

FIG. 6 is a schematic diagram of a system 600 for a magnetic field detection system according to an embodiment of the present invention. The system 600 includes an optical excitation source 610, which directs optical excitation to an NV diamond material 620 with NV centers, or another magneto-optical defect center material with magneto-optical defect centers. An RF excitation source 630 provides RF radiation to the NV diamond material 620.

As shown in FIG. 6, a first magnetic field generator 670 generates a magnetic field, which is detected at the NV diamond material 620. The first magnetic field generator 670 may be a permanent magnet positioned relative to the NV diamond material 620, which generates a known, uniform magnetic field (e.g., a bias or control magnetic field) to produce a desired fluorescence intensity response from the NV diamond material 620. In some embodiments, a second magnetic field generator 675 may be provided and positioned relative to the NV diamond material 620 to provide an additional bias or control magnetic field. The second magnetic field generator 675 may be configured to generate magnetic fields with orthogonal polarizations, for example. In this regard, the second magnetic field generator 675 may include one or more coils, such as a Helmholtz coils. The coils may be configured to provide relatively uniform magnetic fields at the NV diamond material 620 and each may generate a magnetic field having a direction that is orthogonal to the direction of the magnetic field generated by the other coils. For example, in a particular embodiment, the second magnetic field generator 675 may include three Helmholtz coils that are arranged to each generate a magnetic field having a direction orthogonal to the other direction of the magnetic field generated by the other two coils resulting in a three-axis magnetic field. In some embodiments, only the first magnetic field generator 670 may be provided to generate a bias or control magnetic field. Alternatively, only the second magnetic field generator 675 may be provided to generate the bias or control magnetic field. In yet other embodiments, the first and/or second magnetic field generators may be affixed to a pivot assembly (e.g., a gimbal assembly) that may be controlled to hold and position the first and/or second magnetic field generators to a predetermined and well-controlled set of orientations, thereby establishing the desired bias or control magnetic fields. In this case, the controller 680 may be configured to control the pivot assembly having the first and/or second magnetic field generators to position and hold the first and/or second magnetic field generators at the predetermined orientation.

The system 600 further includes a controller 680 arranged to receive a light detection or optical signal from the optical detector 640 and to control the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675. The controller may be a single controller, or multiple controllers. For a controller including multiple controllers, each of the controllers may perform different functions, such as controlling different components of the system 600. The second magnetic field generator 675 may be controlled by the controller 680 via an amplifier 660, for example.

The RF excitation source 630 may be a microwave coil, for example. The RF excitation source 630 is controlled to emit RF radiation with a photon energy resonant with the transition energy between the ground m_(s)=0 spin state and the m_(s)=±1 spin states as discussed above with respect to FIG. 3.

The optical excitation source 610 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 610 induces fluorescence in the red from the NV diamond material 620, where the fluorescence corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 620 is directed through the optical filter 650 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the optical detector 640. The optical excitation light source 610, in addition to exciting fluorescence in the NV diamond material 620, also serves to reset the population of the m_(s)=0 spin state of the ground state ³A₂ to a maximum polarization, or other desired polarization.

The controller 680 is arranged to receive a light detection signal from the optical detector 640 and to control the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675. The controller may include a processor 682 and a memory 684, in order to control the operation of the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675. The memory 684, which may include a nontransitory computer readable medium, may store instructions to allow the operation of the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675 to be controlled. That is, the controller 680 may be programmed to provide control.

Detection of Magnetic Field Changes

As discussed above, the interaction of the NV centers with an external magnetic field results in an energy splitting between the m_(s)=−1 spin state and the m_(s)=+1 spin state that increases with Bz as shown in FIG. 4, for example. The pair of frequency responses (also known as Lorentzian responses, profiles, or dips) due to the component of the external magnetic field along the given NV axis manifest as dips in intensity of the emitted red light from the NV centers as a function of RF carrier frequency. Accordingly, a pair of frequency responses for each of the four axes of the NV center diamond lattice result in an energy splitting between the m_(s)=−1 spin state and the m_(s)=+1 spin state that corresponds to the component of the external magnetic field along the axis for a total of eight Lorentzian profiles or dips, as shown in FIG. 5. When a bias magnetic field is applied to the NV diamond material (such as by the first and/or second magnetic field generators 670, 675 of FIG. 6), in addition to an unknown external magnetic field existing outside the system, the total incident magnetic field may thus be expressed as B_(t)(t)=B_(bias)(t) B_(ext)(t), where B_(bias)(t) represents the bias magnetic field applied to the NV diamond material and B_(ext) (t) represents the unknown external magnetic field. This total incident magnetic field creates equal and linearly proportional shifts in the Lorentzian frequency profiles for a given NV axis between the m_(s)=−1 spin state and the m_(s)=+1 spin state relative to the starting carrier frequency (e.g., about 2.87 GHz).

Because the applied bias magnetic field B_(bias)(t) is already known and constant, a change or shift in the total incident magnetic field B_(ext)(t) will be due to a change in the external magnetic field B_(ext)(t). To detect a change in the total incident magnetic field, the point of greatest sensitivity in measuring such a change will occur at the point where the frequency response is at its largest slope. For example, as shown in FIG. 7, an intensity response I(t) as a function of an RF applied frequency f(t) for a given NV axis due to a magnetic field is shown in the top graph. The change in intensity I(t) relative to the change in RF applied frequency,

$\frac{{l(t)}}{f},$

is plotted against the RF applied frequency f(t) as shown in the bottom graph. Point 25 represents the point of the greatest gradient of the Lorentzian dip 20. This point gives the greatest measurement sensitivity in detecting changes in the total incident magnetic field as it responds to the external magnetic field.

The Hyperfine Field

As discussed above and shown in the energy level diagram of FIG. 2, the ground state is split by about 2.87 GHz between the m_(s)=0 and m_(s)=±1 spin states due to their spin-spin interactions. In addition, due to the presence of a magnetic field, the m_(s)=±1 spin states split in proportion to the magnetic field along the given axis of the NV center, which manifests as the four-pair Lorentzian frequency response shown in FIG. 5. However, a hyperfine structure of the NV center exists due to the hyperfine coupling between the electronic spin states of the NV center and the nitrogen nucleus, which results in further energy splitting of the spin states. FIG. 8 shows the hyperfine structure of the ground state triplet ³A₂ of the NV center. Specifically, coupling to the nitrogen nucleus ¹⁴N further splits the m_(s)=±1 spin states into three hyperfine transitions (labeled as m₁ spin states), each having different resonances. Accordingly, due to the hyperfine split for each of the m_(s)=±1 spin states, twenty-four different frequency responses may be produced (three level splits for each of the m_(s)=±1 spin states for each of the four NV center orientations).

Each of the three hyperfine transitions manifest within the width of one aggregate Lorentzian dip. With proper detection, the hyperfine transitions may be elucidated within a given Lorentzian response. To detect such hyperfine transitions, in particular embodiments, the NV diamond material 620 exhibits a high purity (e.g., low existence of lattice dislocations, broken bonds, or other elements beyond ¹⁴N) and does not have an excess concentration of NV centers. In addition, during operation of the system 600 in some embodiments, the RF excitation source 630 is operated on a low power setting in order to further resolve the hyperfine responses. In other embodiments, additional optical contrast for the hyperfine responses may be accomplished by increasing the concentration of NV negative-charge type centers, increasing the optical power density (e.g., in a range from about 20 to about 1000 mW/mm²), and decreasing the RF power to the lowest magnitude that permits a sufficient hyperfine readout (e.g., about 1 to about 10 W/mm²).

FIG. 9 shows an example of fluorescence intensity as a function of an applied RF frequency for an NV center with hyperfine detection. In the top graph, the intensity response I(t) as a function of an applied RF frequency f(t) for a given spin state (e.g., m_(s)=−1) along a given axis of the NV center due to an external magnetic field is shown. In addition, in the bottom graph, the gradient

$\frac{{l(t)}}{f}$

plotted against the applied RF frequency f(t) is shown. As seen in the figure, the three hyperfine transitions 200 a-200 c constitute a complete Lorentzian response 20 (e.g., corresponding to the Lorenztian response 20 in FIG. 7). The point of maximum slope may then be determined through the gradient of the fluorescence intensity as a function of the applied RF frequency, which occurs at the point 250 in FIG. 9. This point of maximum slope may then be tracked during the applied RF sweep to detect movement of the point of maximum slope along the frequency sweep. Like the point of maximum slope 25 for the aggregate Lorentzian response, the corresponding movement of the point 250 corresponds to changes in the total incident magnetic field B_(t), which because of the known and constant bias field B_(bias)(t), allows for the detection of changes in the external magnetic field B_(ext) (t).

However, as compared to point 25, point 250 exhibits a larger gradient than the aggregate Lorentzian gradient described above with regard to FIG. 7. In some embodiments, the gradient of point 250 may be up to 1000 times larger than the aggregate Lorentzian gradient of point 25. Due to this, the point 250 and its corresponding movement may be more easily detected by the measurement system resulting in improved sensitivity, especially in very low magnitude and/or very rapidly changing magnetic fields.

The embodiments of the inventive concepts disclosed herein have been described in detail with particular reference to preferred embodiments thereof, but it will be understood by those skilled in the art that variations and modifications can be effected within the spirit and scope of the inventive concepts. 

What is claimed is:
 1. A system for magnetic detection, comprising: a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers; a radio frequency (RF) excitation source configured to provide RF excitation to the NV diamond material; an optical excitation source configured to provide optical excitation to the NV diamond material; an optical detector configured to receive an optical signal emitted by the NV diamond material, wherein the optical signal is based on hyperfine states of the NV diamond material; and a controller configured to detect a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.
 2. The system of claim 1, wherein the controller is configured to detect a point of the largest gradient of the optical signal based on the hyperfine states.
 3. The system of claim 1, wherein the controller is further configured to: detect a movement of the gradient of the optical signal based on the hyperfine states emitted by the NV diamond material; and compute a total incident magnetic field at the NV diamond material based on the movement of the gradient.
 4. The system of claim 1, wherein the RF excitation source is configured to provide the RF excitation at a low power.
 5. The system of claim 1, further comprising a magnetic field generator configured to generate a bias magnetic field, wherein the controller is further configured to detect a plurality of gradients of the optical signal based on the hyperfine states for a plurality of NV center orientations.
 6. The system of claim 1, further comprising a magnetic field generator configured to generate a magnetic field, wherein the controller is further configured to control the magnetic field generator to generate a bias magnetic field and to detect a plurality of gradients of the optical signal based on the hyperfine states for a plurality of NV center orientations.
 7. A system for magnetic detection, comprising: a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers; means for providing a radio frequency excitation to the NV diamond material; means for providing optical excitation to the NV diamond material; means for receiving an optical signal emitted by the NV diamond material, wherein the optical signal is based on hyperfine states of the NV diamond material; and means for detecting a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.
 8. The system for magnetic detection of claim 7, wherein the means for detecting a gradient of the optical signal based on the hyperfine states detects a point of the largest gradient of the optical signal.
 9. The system for magnetic detection of claim 7, further comprising means for generating a bias magnetic field, and wherein the means for detecting a gradient of the optical signal based on the hyperfine states detects a plurality of gradients of the optical signal for a plurality of NV center orientations.
 10. A method for increasing measurement sensitivity of a magnetic detection system having a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers, comprising: applying RF excitation to the NV diamond material; applying optical excitation to the NV diamond material; measuring an optical signal emitted by the NV diamond material, wherein the optical signal emitted by the NV diamond is based on hyperfine states of the NV diamond material; and detecting a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.
 11. The method of claim 10, further comprising: detecting a movement of the gradient of the optical signal based on the hyperfine states emitted by the NV diamond material; and computing a total incident magnetic field at the NV diamond material based on the movement of the gradient.
 12. The method of claim 10, wherein the detected gradient is a point of the largest gradient of the optical signal based on the hyperfine states.
 13. The method of claim 10, wherein the RF excitation is applied at a low power.
 14. The method of claim 13, wherein the RF excitation is applied at a power ranging from about 1 to about 10 W/mm².
 15. The method of claim 13, further comprising: applying a bias magnetic field; and detecting a plurality of gradients of the optical signal based on the hyperfine states for a plurality of NV center orientations.
 16. A system for magnetic detection, comprising: a magneto-optical defect center material comprising a plurality of magneto-optical defect centers; a radio frequency (RF) excitation source configured to provide RF excitation to the magneto-optical defect center material; an optical excitation source configured to provide optical excitation to the magneto-optical defect center material; an optical detector configured to receive an optical signal emitted by the magneto-optical defect center material, wherein the optical signal is based on hyperfine states of the magneto-optical defect center material; and a controller configured to detect a gradient of the optical signal based on the hyperfine states emitted by the magneto-optical defect center material.
 17. The system of claim 16, wherein the controller is configured to detect a point of the largest gradient of the optical signal based on the hyperfine states.
 18. The system of claim 16, wherein the controller is further configured to: detect a movement of the gradient of the optical signal based on the hyperfine states emitted by the magneto-optical defect center material; and compute a total incident magnetic field at the magneto-optical defect center material based on the movement of the gradient.
 19. The system of claim 16, wherein the RF excitation source is configured to provide the RF excitation at a low power.
 20. The system of claim 16, further comprising a magnetic field generator configured to generate a bias magnetic field, wherein the controller is further configured to detect a plurality of gradients of the optical signal based on the hyperfine states for a plurality of magneto-optical defect center orientations.
 21. The system of claim 16, further comprising a magnetic field generator configured to generate a magnetic field, wherein the controller is further configured to control the magnetic field generator to generate a bias magnetic field and to detect a plurality of gradients of the optical signal based on the hyperfine states for a plurality of magneto-optical defect center orientations. 